Referring now to the drawings, wherein the use of a strut is shown, FIG. 1 illustrates a work vehicle 100 which can be, for example, an off-highway truck 102. The truck has at least one front and rear strut 104, 106 disposed in supporting relation to a material carrying portion 108 of the work vehicle 100. The preferred embodiment has two front and two rear struts which are the gas-over-liquid type commonly known in the industry. It is sufficient in the understanding of the load monitoring system 110 to recognize that the pressure of the fluid, determined by the use of a pressure sensor such as 142, is indicative of the magnitude of the load applied to the strut 104, 106 and that wide swings in the strut pressures are normal and even expected during actual movement of the loaded work vehicle over terrain known as “roading”. Moreover, a strut which has lost pressure and collapsed shows little response to “roading” with significantly less variation in strut pressure. Conversely, an underinflated tire will increase the frequency of the strut pressure variations within the strut supporting that tire. The underinflated tire has a lower spring coefficient than a properly inflated tire and will resultantly increase the oscillatory response of the suspension with corresponding variations in the damping strut pressure.
The load carrying portion 108 includes a vehicular frame 112 and dump body 114. The dump body 114 is connected to the frame 112 by pivot pin 116 and a hydraulic cylinder 118 such that the contents of the dump body 114 can be removed by controllably pressurizing the cylinder 118 to effect pivotal movement of the dump body 114 about the pivot pin 116. In the transport mode, the cylinder 118 is not pressurized and the weight of the dump body is transferred to the frame through the pivot pin 116 and a support pad 120 fixed to the frame 112.
The work vehicle 100 further includes a ground engaging portion 122 and a suspension means 124 for supporting the load carrying portion 108 in a manner to provide damped oscillatory motion between the ground engaging portion 122 and the load carrying portion 108, thereby reducing the transference of loads and the creation of associated stresses from the ground engaging portion 122, to the suspension means 124, and eventually to the frame 112. The suspension means 124 includes a rear axle housing 126 and an A-frame moment arm 128. The A-frame moment arm 128 has a first end portion 130 pivotally connected to the vehicular frame 112 by a socket 132 and a second end portion 134 fixedly connected to the rear axle housing 126. The first end portion 40 of the A-frame moment arm 128 is a king bolt arrangement, substantially spherical in shape and retained from lateral movement by the socket 132. The rear strut 106 has a first end portion 136 pivotally connected to the vehicular frame 112 and a second end portion 138 pivotally connected to the second end portion 134 of the A-frame moment arm 128. Under load, the rear strut will compress.
Similarly, the front strut 104 will be compressed as the load increases; however, the front strut is connected directly between the frame 112 and a front axle housing 140. A more straightforward relationship exists here in that a force F experienced by the front strut 104 can be determined by measuring the internal pressure of the strut 104, subtracting the front strut pressure corresponding to an unloaded truck, and multiplying the pressure by the area of the strut 104. The reaction force F between the ground engaging portion 122 and the work surface is substantially equivalent to the force F experienced by the front strut 104.
Even though there are alerts when a truck strut is overloaded such as those associated with load monitoring systems, the situation is not always corrected. Operation of the vehicle with a collapsing strut will have obvious effects on the accuracy of the payload monitor owing to the change in the relationship between strut pressure and payload. Other serious consequences also result from such operation. For example, uneven tire wear is an undesirable result of extended vehicle operation with a collapsed strut. Tires are a major operating expense of off-highway trucks and any change in their replacement schedule can have serious impact on profitability. Thus, a collapsed strut can have economic impact other than replacement of the damaged strut. Moreover, a completely collapsed strut results in repeated metal-to-metal contact and the possibility of eventual major structural failure. Frame damage can occur after relatively short periods of operation and the resultant repair costs can be exorbitant.
There are other causes for a collapsed strut other than overloading. For example, struts of various sorts for various types of vehicles may have different working fluids contained in them for the absorption of shock. Often, the cylinders of struts includes a combination of gas and fluid, such as air over oil, air over hydraulic fluid, nitrogen over oil, etc. A typical mixture is hydraulic oil that is used with nitrogen. The separation of the gas from the liquid is important in struts as gas is compressible while the liquid is not. If too much of the gas is entrained into the liquid or otherwise escapes from the cylinder, then the liquid is effectively the only substance present for absorbing the shock. It is not unusual for 60 to 80% of the nitrogen to eventually be entrained into the oil. Unfortunately, liquid such as oil or hydraulic fluid is incompressible; and therefore, is not ideally suitable for absorbing shock as it is instead an effective medium for transferring shock to the frame. Also, when a vehicle is overloaded, the oil and nitrogen will force their way past the seals of the cylinder, reducing the ability of the strut to absorb shock.
For all the above reasons, it is desirable to develop a better strut construction than has yet been devised.